The present invention relates to a dielectric ceramics and more particularly relates to such ceramics having high dielectric constant, high unloaded Q value and high stability against temperature variations so as to be advantageous to use in microwave circuits.
Conventionally, in the microwave frequency ranges, dielectrics have been applied for impedance matching in the microwave circuits and producing dielectric resonators, etc. Particularly, with the recent progress in the technique for integration of microwave circuits, there has been a strong demand for small-sized dielectric resonators as oscillator frequency stabilizers, frequency filters, etc., and therefore for materials having high dielectric constant and low microwave loss with sufficient stability against temperature variations, to be used, for example, as substrates for integrated circuits.
As material for dielectric resonators, various compositions, for example, compositions of the BaO-TiO.sub.2 group, compositions prepared by substituting other elements for part of BaO-TiO.sub.2 group, or compositions prepared by combining TiO.sub.2 whose dielectric constant has negative temperature variation rate, with dielectric compositions whose dielectric constant has a positive temperature coefficient, have been mainly employed. Those compositions, however, are still unsatisfactory from a practical standpoint because they have such drawbacks as large dielectric loss, large temperature variations with respect to the dielectric constant, large deviations in the temperature variation rate of the dielectric constant, etc.
As an improved material for the above-mentioned purpose, we previously invented ceramics having the composition xBaO.yNa.sub.2.zNb.sub.2 O.sub.5 wherein 0.593.ltoreq.x.ltoreq.0.762, 0.04.ltoreq.y.ltoreq.0.13, 0.174.ltoreq.z.ltoreq.0.32, and x+y+z=1, which can be employed to produce superior dielectric microwave resonators. However these ceramics are still unsatisfactory because of low stability against temperature variations.